The following abbreviations and terms are herewith defined:
3GPPthird generation partnership projectACKacknowledgementDLdownlinkDTXdiscontinuous transmissioneNBBase Station/Node B of an LTE systemE-UTRANevolved UTRANFDD:frequency division duplexH-ARQhybrid automatic repeat (or retransmission) requestLTElong term evolution of 3GPP (also known as 3.9G)MCSmodulation and coding set (or scheme)MIMOmultiple input multiple output (related to antenna configuration)NACKnegative ACKNode B base station or similar network access nodeOFDMorthogonal frequency division multiplexPDCCHphysical downlink control channelPDSCHphysical downlink shared channelPMIprecoding matrix indexPRBphysical resource blockPUCCHphysical uplink control channelPUSCHphysical uplink shared channelTDDtime division duplexUEuser equipment (e.g., mobile equipment/station)ULuplinkUMTSuniversal mobile telecommunications systemUTRANUMTS terrestrial radio access network
3GPP is standardizing the long-term evolution (LTE) of the radio-access technology which aims to achieve reduced latency, higher user data rates, improved system capacity and coverage, and reduced cost for the operator. The current understanding of LTE relevant to these teachings may be seen at 3GPP TR 36.213 v8.3.0 (2008-05) entitled PHYSICAL LAYER PROCEDURES (RELEASE 8), which is attached to the priority document as Exhibit A. Both FDD and TDD are considered in LTE, and the non-limiting examples of the invention detailed below are described within the context of the TDD mode.
Allocations of radio resources are given in LTE on the PDCCH. A particular UE listens to the PDCCH at its designated time and sees if it is allocated UL and/or DL resources. If this is the case, the UE maps the allocation information in the PDCCH to the PDSCH or PUSCH as the case may be. In the case of an UL allocation, the UE sends its data on the allocated UL resource and maps that resource to a control channel where it listens for the eNB's ACK/NACK for the UL data. In the case of a DL allocation, the UE tunes to the mapped DL resource and monitors for data from the eNB, and maps that DL resource to a control channel where it then sends its ACK/NACK for the DL data (specifically, the lowest control channel element index of the PDCCH which carries the DL control information DCI maps to the UL channel which carries the ACK/NACK). Each PDCCH gives multiple allocations, and the typical scenario is that there will be more DL allocations than UL in a given PDCCH. These teachings assume that typical scenario.
LTE reduces control signalling in certain instances as compared to prior wireless protocols in order to conserve radio resources for the transfer of user data, and also to more efficiently use the UE's limited power supply. As noted above, LTE allows a frame configuration in which there are more DL subframes than UL subframes, which causes difficulty for one-to-one mapping of the allocated resource to its ACK/NACK. One way to address these issues is to send a single ACK/NACK for data received over a group of DL resources. Reference in this regard may be had to document R1-081110 (3GPP TSG-RAN WG1 #52, Sorrento, Italy, Feb. 11-15, 2008, by Ericsson, Motorola, Nokia, Nokia Siemens Networks and Qualcomm) entitled Multiple ACK/NACK for TDD and attached to the priority document as Exhibit B. That document states that for LTE it is agreed that UL hybrid-ARQ acknowledgements in TDD can be transmitted as a single ACK/NACK feedback where ACK/NACKs from one or several DL subframes are combined. This is termed ‘bundling’ the ACKs/NACKs, and is performed by a logical AND operation on the ACKs/NACKs for the various DL resources to generate a single ACK/NACK report, which allows the PUCCH formats already defined for LTE to be reused (PUCCH Format 1/1A/1B). This ACK/NACK mode has broadly been named “AN-bundling” (where AN is short for ACK/NACK). It is to be hard-coded (from specifications; e.g., TS 36.213 at Exhibit A of the priority document) as to which DL subframes are jointly acknowledged in which UL subframe, and thus depends on which TDD configuration is active.
When a UE is configured for dual layer reception (e.g. MIMO), it carries two bits on its uplink ACK/NACK channel. These bits are needed to acknowledge each of the layers (the term layers and streams are used interchangeably). However, if the UE is not assigned exactly the same PRB resources (or transmission parameters) in all subframes within the ACK/NACK bundling window it will have limited correlation between subframes for a certain layer (or stream), in which case a bundled ACK/NACK of such stream becomes meaningless.
The inventors have recognized this previously and determined that for the above case it would be better to use those two bits for creating smaller sub-bundling windows to achieve a gain. Such sub-bundling has been described for single stream case by the inventors in U.S. Provisional Patent Application Ser. No. 61/029,361 entitled “Virtual Dual-Stream Transmission to Reduce PDCCH Reliability Problem for Downlink-Heavy LTE TDD”, attached to the priority document as Exhibit C.
The above-referenced provisional patent application considers how to configure a UE to do virtual dual-stream transmission and describes that it could be integrated with MIMO. Higher layer configuration may be used in order to optimize the use of the bits.